Effect of Dietary Supplementation With Omega-3 Fatty Acids on Human Sperm Characteristics, a Preliminary Study

The phospholipids of mammalian spermatozoa possess a distinctive and highly unusual fatty acid composition, the most unique feature of which is a very high proportion of long chain (C20-22) highly polyunsaturated fatty acyl groups. In most mammals, docosahexaenoic acid (DHA; 22:6,n-3) is the dominant polyunsaturated fatty acid (PUFA) although, in several species, docosapentaenoic acid (22:5,n-6) is also a major component 2. The lipid composition is a major determinant of the membrane flexibility required for the characteristic flagella movement of spermatozoa and for the fusogenic properties of the membranes associated with the acrosome reaction and fertilization. In addition, it has been demonstrated that lipid-derived mediators are involved in various signal transduction mechanisms that regulate spermatozoa functions.

Sperm motility was therefore closely correlated with fertility, yet factors controlling sperm motility in humans are not fully understood 12. The amount of PUFA, mainly DHA, and to a lesser extent eicosapentaenoic acid (EPA), was showed to be positively associated with sperm motility and essential for optimal fertility. The reduction in the amount of DHA in sperm lipids have been correlated with reduced sperm concentration, sperm progressive motility and the proportion of cells with normal morphology. In asthenozoospermic (poor sperm forward motility), the levels of DHA (and total PUFA) was found to be lower than in normozoospermic individuals despite similar serum fatty acid composition 18. Broiler spermatozoa rich in EPA or DHA or both showed significantly increased fertility following artificial insemination (AI).

Chilling injury to mammalian gametes has been described as the irreversible damage that occurs upon cooling to low, but non-freezing, temperatures. Several studies suggested that chilling injury is the major limiting factor for successful gamete cryopreservation. Other studies suggested that membranes are the primary sites for structural and functional chilling injury in sperm and oocytes. Additionally, membrane chilling injury is dependent on the biochemical and biophysical properties of membranes. The plasma membrane thermotropic lipid phase transition (Tm) from the fluid liquid crystalline phase to the more rigid gel phase is associated with chilling injury. When membrane lipids undergo lipid phase transition (LPT), fluidity decreases and the structure and functioning of the membrane change. As a result, the membrane permeability increases and the cells are damaged. The temperature at which Tm occurs is greatly affected by the fatty acid composition of the membrane. Membranes consisted of lipids with multiple unsaturations or short carbon chains are more fluid at low temperatures. The ability of the spermatozoal plasma membrane to resist structural damage during cryopreservation may therefore be related to its fatty acids composition and the strength of the bonds between membrane components 38. It was shown, for example, that spermatozoa of Asian elephants, which are more chilling sensitive than African elephant sperm, contain lower concentration of PUFA in their membranes and are especially poor in DHA.

There are several ways to change the chilling sensitivity and Tm in mammalian gametes. Spermatozoa can spontaneously interact with liposomes as was described in several studies. Previous work suggested that phospholipids adsorbed on to the sperm cells, which were then cooled to 4oC, increased the chilling resistance of the sperm cells from bovine, ram and elephant.

The relationship between dietary components and reproduction is well established. Follicular maturation, ovulation and oestrus in the female, and libido and fertility in the male, might all be adversely affected by undernutrition. Men with infertile semen were found to consume less omega-3 fatty acids than fertile men, and a significant correlation was established between the consumption of alpha-linolenic acid (18:3n-3) on the one hand and sperm concentration and progressive motility on the other hand. In boar, the output of the accessory glands, but not the output of spermatozoa by the testes, was affected by the reduced feed intake and is likely to reflect a suppression of androgen secretion. Various reports showed that enrichment of diet with PUFA can alter the biophysical properties or reproductive performance of mammalian and avian sperm and oocytes.